On Jason Sheet's blog, there's a new post that offers up a brief tutorial on implementing the soundex functionality in PHP.
Soundex is an algorithim to help determine if a word sounds like another word; it is commonly used to detect words that are incorrectly spelled or to make the suggestion "did you mean ? instead of !?" For example if you typed in smythe using soundex a program could look for other names that sound like it and find that smith and smythe sound alike.
In this article I will demonstrate a PHP implementation of soundex, in practice this implementation has little value because PHP itself has soundex() function already but this article should help you understand how it works better.
He jumps right in, mentioning the steps the script will take (seven of them) before getting right to the code. He's written up his own soundex functionality packaged up nicely in a reusable function and has even compared it to the built-in PHP soundex function for accuracy.